Improved Natural Current Sharing and Phase-Shedding Operation in LLC Resonant Converters With Voltage-Doubler Rectifier

The two-phase LLC resonant converter is widely used in high-power applications. It can reduce the conduction losses and prevent the thermal runaways by sharing the overall output currents. In addition, the converter can operate in single-phase mode by turning off one of the two phases during phase-shedding or fault situations. Consequently, the two-phase LLC resonant converter can achieve high efficiency and high reliability across a wide operating range. However, this topology suffers from a significant unbalanced current caused by component's tolerance. Thus, this article proposes a novel LLC resonant converter to alleviate the unbalanced current. The structure of proposed converter is based on the variable voltage sources and secondary-side point connection. The proposed converter can achieve natural current sharing without multiple current sensors, load share ICs, and complex current control. In addition, it has small current sharing errors and excellent phase-shedding performance through variable voltage sources. The small capacitance of voltage variable sources acts as a current balancer, allowing voltage gain differences caused by the component's tolerance. As a result, the proposed converter can achieve high efficiency and high reliability without any additional components. The feasibility of proposed converter is demonstrated by the experimental results with 100 V/20 A 2000 W lab prototype converters.